I included code to generate on-the-fly both the standard and retina display versions of the keyboard png file, only to find out that, even though the Pythonista UI is retina resolution, scene renders never were.

... If retina will never be available, that's ok - makes for simpler GUI applications (and less processor load) - but I'd love to know for sure, so I can just drop the code to check for it / upscale the image.

Scenes should always be rendered in retina resolution on devices that have retina screens. The coordinate system for retina and non-retina screens is the same however, so that the same code works unmodified on both kinds of screen. oefe is correct, on a retina screen, 1 point equals 2 pixels.